The invention relates to a diplexer for separating a signal current and a supply current. Such a system is used in remotely fed intermediate regenerators or repeaters of broad-band transmission systems with coaxial cable paths. Such systems exhibit a high circulating atenuation at high frequencies. They are provided with an input or output side inductor arrangement for the power supply and a capacitor which connects one of the two power supply terminals of the regenerator or repeater to its reference potential.
A diplexer of the type initially cited is known from German LP No. 12 72 466, incorporated herein by reference. It consists of high and low pass filters connected in series, and is particularly employed for the power supply of remotely fed line repeaters of broad-band carrier frequency systems. They are constructed with the use of coaxial inductors. Given these coaxial inductors, the two windings offer very little resistance to the signal current traversing in the opposite direction, whereas they offer a very high resistance to the noise currents respectively traversing only one winding. Capacitors which exhibit a noticeable inductance at high frequencies are provided for the connection between the reference potential of the repeater and the grounded potential of the outer inductor of the coaxial cable. This inductance vitiates the coupling effect of the capacitor. It results from the lead inductance of the capacitor and the structure caused by the high voltage di-electric strength and therefore cannot be reduced as desired without further efforts. Due to the deteriorated connection of the two grounded potentials, a deterioration of the circulating attenuation also results, i.e. an increased feedback of the output signal of the repeater to its input. The term "circulating attenuation" describes the attenuation between the output side pair of posts and the input side pair of posts. In this case, the circulating attenuation is again increased by means of additionally provided line inductors. However, a further limit derives due to the disruptive leakage inductance of the line inductors occurring at higher inductances.
A further such arrangement is known from the periodical "Frequenz" 28, 1974, Pages 326-333, particularly FIG. 15, incorporated herein by reference, in which ferrite rings and high voltage capacitors are applied in succession on a coaxial cable and the entire arrangement is surrounded by a tubular housing having a conductive connection. Upon employment of coaxial cables, however, an involved and difficult contacting of the capacitors to the inner wall of the tubular housing and to the outer conductor of the coaxial cable results. In view of the high signal frequencies, the proposed contacting by means of springs cannot be employed. Also, a particularly high-grade shielding is required given the cable piece connected to the capacitors and ferrite rings.
A remotely fed intermediate repeater, particularly for coaxial message transmission links disposed between an input side and an output side line connected to one another over an outer conductor connection, is known from U.S. Pat. No. 4,114,107, incorporated herein by reference. In this system, the outer conductor connection and a feed voltage terminal are capacitively connected. The feed voltage terminal also has an alternating voltage-wise reference potential at the same time. In this arrangement, at least one capacitor is provided between the grounded potential of the outer conductor of the coaxial cable and the reference potential of the intermediate repeater. Accordingly, problems concerning the coupling of the input circuit and output circuit over the grounded connections result at higher frequencies. In order to increase the circulating attenuation, the repeater is sub-divided into at least two sub-repeaters whereby the two sub-repeaters are decoupled over a respective capacitor lying between the reference potential of the sub-repeater and the outer conductor potential of the coaxial cable. Moreover, the feed voltage inputs of the sub-repeaters are decoupled from one another in high frequency-wise fashion. In order to increase the circulating attenuation, a line inductor is additionally provided which transmits the useful signal from the input to the output sub-repeater and thereby suppresses noise signals. However, a sure suppression of the noise signals only results when the passage through the outer chamber partition between the two sub-repeaters (the outer chamber partition having the potential of the outer conductor of the cable), has a high capacitance, i.e. is designed as a high voltage stable feed-through capacitor. As a result of these additional feed-through capacitors which are to be provided for each line connection between the two sub-repeaters, however, a high expense results overall given an involved mechanical structure of the repeater arrangement at the same time. Also, due to the parallel connection of the individual line inductors, a reduction of the effective inductance again results overall and thus a reduction of the circulating attenuation occurs. The coupling between the two repeater or generator parts occurs over lines which proceed in a field-filled space so that the possibility of disruptions being scattered-in exists on the one hand, and on the other hand, the required all-around shielding has an influence on the repeater or regenerator properties.